I never said there's a cap for normal typical usage. We're not talking about typical normal web browsing stuff here. Note my original post, "Do not abuse this. AT&T does not consider unlimited as unlimited bandwidth 24x7. They have a cap somewhere where they'll start to warn you and can cut you off for "disrupting their services". Video streaming all day on the iPad 3G would take up more downstream bandwidth than either torrenting or web servers.
AT&T has no way of knowing what users are using on their devices, data is data to them. They have to have a "soft" cap limit somewhere to notify them of an excessive usage, which allows them to send a warning to their users about excessive usage and the potential service cut off if the users don't stop it.
People should not be running around thinking their unlimited plans means that they can do everything they want and there's no limit to it. That's absolutely not true and there is a limit and the agreement already explains majority of it.
Also, why don't you explain to us the uses that's not permitted because it would be using iPad for other than its intentions? Why shouldn't it be running torrents or web servers, to most people it's a tiny computer, not a phone?